Personal computers which have modems for communicating data to other personal computers are in widespread use.
In many situations a person operating a personal computer at one location requires support, guidance or help from another person who is at a different physical locations. Several commercially available computer programs provide a mechanism whereby two computers connected by modem can be made to operate in tandem. That is, whatever appears on the screen of one computer (herein termed the CUSTOMER PC) identically appears on the screen of the other computer (herein termed the SUPPORT PC). Using such a program an expert sitting at the SUPPORT PC can see exactly what is appearing at the screen of the CUSTOMER PC and the expert can therefore easily help or provide guidance to the person operating the CUSTOMER PC. Among the commercial programs that provide this general type of facility for IBM personal computers (and for what are generally termed IBM PC compatible computers) are: (1) A program sold under the trademark, CLOSE-UP, by Norton-Lambert Corp. of Santa Barbara Calif., (2) A program sold under the trademark CO-SESSION by Triton Technologies Inc. of Iselin N.J., and (3) A program sold under the trademark CARBON COPY by Microcom Systems Inc. of Norwood, Mass. Other programs of this type are described in the magazine entitled "PC Magazine" dated Jun 12, 1990.
There are also programs of this type available for the Macintosh personal computer sold by Apple Computer Corp. However, program which operate on the Macintosh always write to the display screen through the BIOS or Display Driver, whereas program for the IBM PC often bypass the BIOS and Screen Driver and write directly to the display, that is, they write directly to the memory that is used to refresh the display. Thus with the IBM PC it is necessary to scan the display (i.e. scan the memory used to refresh the display) to insure that one has detected all changes that have occurred on the screen, whereas with the Macintosh it is merely necessary to intercept or monitor all commands that are sent to the display driver and to transfer these commands between the two computers.
It is possible to quickly transfer screens of character data (or in the case of the Macintosh the commands going to the display driver) from the CUSTOMER PC to the SUPPORT PC; however, it takes considerably more time to transfer a screen (or even a portion of a screen) of graphic information.
The delay in transmitting graphic information between computers is particularly troublesome when the computers are equipped with an input device which requires visual feedback, such as a mouse. With a device such as a mouse, the operator's physical movement is keyed to the image which is seen on the screen. If due to the delay in transmission of images between computers, the operator does not see the result of his physical mouse movement on the display, the operator tends to become confused and to move the mouse an excessive amount thereby overshooting the desired location.